Problem: What is the volume of a cylinder with base radius $3$ and height $9$ ? $3$ $9$
Explanation: The area of the base is simply the area of a circle: $\pi r^2 = \pi \cdot 3^2 = 9 \pi$ The volume of the cylinder is the area of the base times the height: $B \cdot h = 9\pi \cdot 9 = 81\pi$.